Method of manufacturing fine metallic filaments

ABSTRACT

A method of producing a yarn of fine metallic filaments at low cost, which comprises covering a bundle of a plurality of metal wires with an outer tube metal to form a composite wire, drawing said composite wire and then separating the outer tube metal from the core filaments in said composite wire, wherein for ease of said separation treatment, the surfaces of said metal wires are coated with a suitable separator or subjected to a suitable surface treatment before the covering of the outer tube metal, thereby to prevent the metallic bonding of the core filaments to each other in the subsequent drawing or heat-treatment of the composite wire.

United States Patent [191 Takeo et a].

[ METHOD OF MANUFACTURING FINE METALLIC FILAMENTS [75] Inventors:Keinosuke Takeo; I-Iideo Ogita, both of Itami, Japan [73] Assignee:Sumitomo Electric Industries, Ltd.,

Higashi-ku, Osaka, Japan [22] Filed: July 7, 1972 [21] Appl. No.:269,635

[30] Foreign Application Priority Data [451 Apr. 30, 1974 2,718,0499/1955 Prache 29/419 3,529,343 9/1970 Gorton 29/419 FOREIGN PATENTS ORAPPLICATIONS 633,109 12/1961 Canada 29/470.9 820,033 9/ 1959 GreatBritain 29/470.9

Primary ExaminerCharles W. Lanham Assistant Examiner-D. C. Reiley, 111Attorney, Agent, or Firm-Sughrue, Rothwell, Mion Zinn and Macpeak [57]ABSTRACT A method of producing a yarn of fine metallic filaments at lowcost, which comprises covering a bundle of a plurality of metal wireswith an outer tube metal to form a composite wire, drawing saidcomposite wire and then separating the outer tube metal from the corefilaments in said composite wire, wherein for ease of said separationtreatment, the surfaces of said metal wires are coated with a suitableseparator or subjected to a suitable surface treatment before thecovering of the outer tube metal, thereby to prevent the metallicbonding of the core filaments to each other in the subsequent drawing.or heat-treatment of the composite wire. 5

4 Claims, 6 Drawing Figures ATENTEUAPR 30 I974 FIG. 2

FIG I iafis llilL FIG. 5

FIG. 4

METHOD OF MANUFACTURING FINE METALLIC F ILAMENTS DESCRIPTION OF THEINVENTION This invention relates to a process for producing a yarn offine metallic filaments, and especially, to a separator for preventingthe metallic bonding of core filaments from each other in the bundledrawing method.

In recent years, fine metallic wires with a diameter of 0.3 to 0.005 mmmade of such materials as carbon steel, alloy steel or stainless steelhave been used for tire cords, metallic fibers for blending purposes,metallic fibers for filters, etc.

Generally, fine metallic filaments having a diameter of not more than0.25 mm ought to be produced by the repetition of heat-treatment anddrawing in accordance with the single wire drawing process by a die, andmoreover, the yield per unit time is low, which results in a very highcost of production. Therefore, in an attempt to avoid this defect, thebundle drawing process was devised, and has been utilized to someextent.

The conventional bundle drawing method comprises first coating thesurfaces of material wires with a separator, such as metal oxides,graphites or oils, which prevents bonding of wires during drawings andheattreatments, or with a different metal by, for example, plating;inserting a bundle of a plurality of such wires in a tube of a differentmetal or covering the outer peripheries of a bundle of a plurality ofsaid wires with a metallic tape and then welding the seam portion toform a composite wire; subjecting the composite wire to a diameterreduction treatment by drawing and heattreatment, etc. until thediameter of each wire is reduced to a desired value; and then dissolvingthe outer tube metal or the outer tube metal and the coated metal by achemical method thereby to separate the core wires from each other andproduce fine metallic wires.

However, according to the conventional method, it is difficult to selecta solution which dissolvesthe outer tube metal (A) or the outer tubemetal (A) and the coated metal (B) without chemically attacking the finemetallic filaments at all. Furthermore, since the coated metal (B)exists as a very thin layer among the fine metallic filaments, longperiods of time are required in order to dissolve this layerprogressively from outside by the chemical or electro-chemical method.

With a view to remedying such a defect, we completed an invention of aprocess which comprises cutting both sides of the outer tube metal ofthe final composite wire obtained by using material wires coated with aseparator with two cutting bites, applying a pushdown force to the cutsurfaces upwards and downwards in a direction parallel to the cutsurfaces, thereby to continously break the thinnest portions of the cutsurfaces along the axial direction of the wires and thus divide theouter metal tube into two portions, and at the same time, separate theyarn of fine metallic filaments therein continuously and mechanically.This invention was applied for a patent under US. Ser. No. 254,124 filedMay 17, 1972.

In order to perform such a mechanical separation, it

is essential that the core filaments in the final compos ite wire shouldnot adhere intimately to one another,

and be in the readily separable state. The present invention has solvedthis problem.

An object of this invention is to a method of producing fine metallicfilaments, wherein prior to coating an outer tube metal on a bundle of aplurality of the material wires mentioned above, the surfaces of thematerial wires are coated with a suitable separator or subjected to asuitable surface treatment whereby the metallic bonding of the corefilaments to one another is prevented in the subsequent drawing orheat-treatment of the composite wire, and the core filaments arerendered easily separable in the above-mentioned separa-- tiontreatment.

Another object of this invention is to provide a method of producingfine metallic filaments, in which a mechanical separation treatment canbe performed instead of the conventional chemical treatment in theabove-mentioned separation treatment, thereby producing products of goodquality free from breakage or deterioration in properties without thecorrosion of the fine metallic filaments themselves.

Still another object of this inventionis to provide a method ofproducing brass-plated fine steelfilaments of good quality, in whichprior to coating a bundle of brass-plated steel wires with an outer tubemetal, a separator containing zinc powders is coated on the surfaces ofsaid steel wires, thereby to prevent the evaporation of the zinccomponent of the brass-plated layer during the heat-treatment of thecomposite wire.

In order to achieve these objects, the surfaces of said materials wiresare coated with a suitable separator by a suitable method or subjectedto a suitable surface treatment, prior to coating an outer tube metal ona bundle of the material wires.

According to this invention, the fine powders of clay minerals or porousminerals such as diatomaceous earth are kneaded with a binder such assodium silicate or an organic binder and asuitable liquid as a solventfor the binder; and the resulting kneaded mixture having a suitableviscosity is coated on the surfaces of the material wires and thenheated to evaporate moisture and the binder substance. Then, an outertube metal is covered on a bundle of these material wires, and acomposite wire is produced by the bundle drawing method,

after which the above-mentioned mechanical separation is renderedpossible.

The above and other objects, features and advantages of this inventionwill become fully clear as the description proceeds with reference tothe accompanying drawings. Some embodiments of the invention will bedescribed with reference to the drawings, but the invention is in no waylimited thereto.

FIGS. 1, 2 and 3 aresectional views of wires showing one example of theproductional process for the fine metallic filaments in accordance withthe present invention, FIG. 1 showing the composite wire before drawing,FIG. 2 showing the composite wire after drawing, and FIG. 3 showing finemetallic filaments obtained as final product.

FIG; 4 is a schematic view of the crystal structure of a pyrophilitetype mineral used as the separator in the present invention.

FIG. 5 is a schematic view of the crystal structure of a kaolinitemineral used as the separator.

FIG. 6 is a perspective view showing one example of a coating tank usedfor the coating of the separator compound.

The inventors of the present invention have found that the following sixconditions are necessary for a separator to be used in the bundledrawing process.

a. lt should prevent the bonding of the outer tube metal and the corewires and the bonding of core wires to one another during the drawing ofthe composite wire.

b. The separator should not be bonded to itself during the drawingprocess.

The above two conditions are necessary for the separation of finemetallic filaments after drawing of the composite wire.

c. The frictional force between the separator particles and thefrictional force between the separator and the metal should be greaterthan a certain value.

Usually, when a workpiece is drawn by a die, it undergoes a compressionstress from the wall of the die and a shearing stress owing to frictionbetween the workpiece and the wall of the die in a direction opposite tothe drawing direction, and as a result, is deformed. If the workpiece isan ordinary simple material such as rod or wire, these stress aresmoothly transmitted to the inside of the workpiece, and deformation iseffected. But when the workpiece is a composite composed of an outertube metal and several tens to several hundreds fine wires of smallsectional areas, the transmission of these deformation stresses dependupon the frictional force acting between the outer tube metal and thewires in contact with the inside surface of the tube metal and alsobetween the contacting wires. When this frictional force is small, thestress coming from the die is not fully transmitted to the core wires,but only the outer tube metal is plastically deformed. In this case,there is little or no compression stress from the die to the wiresinside, and therefore, they merely undergo a simple tensile stress.Because of this, tensile fracture occurs as the processing proceeds. Inother words, since the outer tube metal can be deformed, but the wiresinside undergo tensiled fracture, it is impossible to continue thedrawing operation. Furthermore, this phenomenon is not dependent only onthe amount of the frictional force between the wires, but has a closerelation with the deformation resistance, and the thickness of the outertube metal and the core wire metal, the ratio of sectional area betweenthese two metals, the die angle and the pass reduction degree, etc.

To cite an example, a composite wire is produced by inserting 90aluminum wires 0.5 mm in diameter coated with a vegetable oil as theseparator in a copper tube having an outer diameter of 12.5 mm and athickness of 2.25 mm. The vegetable oil acts as a lubricant; and thefrictional forces between the outer tube metal and the aluminum wires,and between the aluminum wires are very small. But both the copper andaluminum have a small resistance to deformation, and the deformationresistance of aluminum is especially small. Thus, it is possible to drawthis composite wire by a die until the diameter is reduced to 0.4 mm.

On the other hand, when the same outer tube metal and vegetable oil asused above are employed, and carbon steel wires of the same diameter areinserted, the composite wire can be processed to an outer diameter ofthe composite wire of 7.3 to 7.1 mm at which point all the wiresgeometrically come into contact, and the inner surface of the outer tubemetal also comes into contact with the wires. However, attempts to drawthe composite wire to a smaller outer diameter for which plasticdeformation of core wires is necessary result in the tensile fracture ofthe core wires or breakage of the outer tube metal, thus making itimpossible to continue the drawing process. This is due to a smallfrictional force. Accordingly, having a close relation with theconstruction of the material, etc., the separator should impart asuitable frictional force between the wires.

d. The particles of the separator should become smaller in size with theprocessing of the composite wire, thereby reducing the thickness of theseparator layer.

When a composite wire consisting of an outer tube metal and wires coatedwith a separator is drawn by a die, its sectional area becomes smalllerand its length becomes larger. The surface area of each core wireincreases in inverse proportion to the diameter of the composite wire.At this time, the separator layer should be progressively decreased inthickness without break. For this purpose, the separator particles needto be divided to smaller particles as the drawing process proceeds. Thereduction in thickness can also be effected by the plastic deformationof the particles. However, the plastic deformation is liable to causebonding of the particles with one another, and therefore, is notdesirable as being contradictory to the requirements (a) and (b)mentioned above.

Accordingly, in order for a given separator compound to be divided intosmall particles, it is desirable that the compound should be soft andhave cleavability. Or the separator should be soft and porous particles,and be divided into fine particles by a compression stress, a shearingstress, etc.

This requirement is partly inconsistent with the requirement (c).Graphite or molybdenum disulfide has a very strong cleavability, andbecause of this, is used as a solid lubricant. But because of itsexcessively good lubricating properties, such a compound cannot givefrictional force to a metal having high deformation resistance such assteel.

Therefore, as mentioned in (0) above, the separator should be chosen sothat it meets both of the requirements (0) and (b) having regard to theconstruction of the material to be used (such as the deformationresistance of the workpiece).

(e) When heat-treatment is required during the drawing of the compositewire, the separator should not be thermally degraded or should notchange the properties mentioned in requirements (a) to (d) upon reactionwith the metal surface of the outer tube metal or the core wires.Furthermore, a gas ascribable to the thermal decomposition of water ofcrystallization, adsorbed water, or the like contained in the separatorshould not be evolved.

When a gas is evolved during the heat-treatment, especially in the caseof the thermal decomposition of a solid such as water ofcrystallization, an abrupt expansion of volume accompanies, and causesan increase in the pressure inside the composite wire. If this pressureexceeds the strength of the outer tube metal, the tube is broken, orlocally expands even if breakage does not occur. Such a phenomenoncauses a trouble in the subsequent drawing process, and becomes thecause of the breakage of the wires or the separation of the outer tubemetal during the processing operation.

We have taken these requirements (a) to (e) into consideration, andfound that readily available and inexpensive substances to be describedare effective as separators, especially for use with metals of highstrength such as steel.

a. Powders of minerals having a pyrophilite-type crystal structure.

The crystal structure of a pyrophilite-type is shown in FIG. 4. Such asubstance having a three-layered structure has cleavability, and theparticles of its powder are in the form of scale-like fragments. This isa relatively soft substance, and does not possess lubricating propertiesdue to cleaving so high as in the case of molybdenum disulfide. Thissubstance therefore well meets the requirements of the separatormentioned above.

b. Powders of montmorillonite minerals.

The crystal structure of this mineral is based on the pyrophilite typein which a part of the Si atom is re-' placed by Al and a part of the Alatom is replaced by Mg, and Na comes into among the lattices. Theseminerals also have properties of a separator as in (a) above.

c. Powders of kaolinite mineralsv has the property of being collapsed tosmall particles on application of force. It is chemically inert, and issuitable as a separator.

The properties of typical minerals which come within the minerals givenin (a) to ((1) above are shown in Table 1. These substances areconverted to far finer particles by their cleavability or by pressuredue to their porosity and form a thin layer. They further exhibit asuitable frictional force, and meet the other requirements of aseparator.

When these substances are used as a separator, they are converted topowders having a size of 300 to 200 mesh (mainly of a particle diameterof about 1 to 5 microns), and coated on the surfaces of the materialwires by a suitable method to be described. When the composite wireobtained by inserting these core wires in an outer tube metal isheat-treated, the temperature should be below the decompositiontemperature of the water of crystallization shown in Table 1. Since amontmorillonite mineral and diatomaceous earth contain adsorbed water,it should be heated and dried at a temperature above the temperature(100 to 200C.) at

which adsorbed water is released.

Decomposition temperature Hardof water of Specific ness cyrstallizationType Name of mineral Chemical formula gravity (Morse) C.)

. Mg (Si4O1o)(OH)2 2.83 1 901,000 Pymphlhte mmemls Tale --i l s i rcgmor r% z 2. 82 1-1.5 600-700 Bentonite.... g 2( i, 4 1D 2 1. 2. 5-2. 6850-900 Montmonuomte ""{Acid claya part of AL and Si is substitu d byullfifs earth Mg and Al). 1 2 61 2 2 5 520 57 a0 nite O K3011 numerals{Nacrite Al2(Si O )(OI-I)4 2.58 2. 5-3 550-100 Dickite 2. 59 2. 5-3600-700 Porous minerals- Diatomaceous earth... SiOz 2.1-2.5

1 No water of crystallization; heat-treatment up to 950 C. possible.

Diatomaceous earth is composed of the siliceous skeletons of deadunicellular aquatic plants called diatoms. Diatomaceousearth consistingessentially of hydrous amorphous silica has an innumerable number ofpores with a diameter of about one micron or less, and

The method of coating the separator on the material wires will bedescribed.

The separator should be coated in a uniform thickness on the surfaces ofmaterial wires prior to coating an outer tube metal on a bundle of thematerial wires. Powders of the separator compound cannot be directlycoated on the surfaces of the material wires. The powders of theseparator should be kneaded with a adhesive substance (binder) and aliquid or a adhesive liquid in order to impart adhesiveness against thematerial wires. We have found that the use of (1) an organic compoundsuch a methyl cellulose, glycerine, polyvinyl alcohol or carboxymethylcellulose and (2) water glass as the binder is very effective.

The properties required of the binder, of course, include one wherein akneaded mixture of powders of a separator, the binder and the liquidshould be readily coated on material wires. Also, the binder should notdamage the processability of composite wire during drawing, nor impairthe effect of the separator by degenerating it, nor injure or degeneratethe surfaces of the core wires, nor cause gas decomposition at theheat-treating of the composite wire. However, most of the substanceshaving adhesiveness or cohesion at room temperature are decomposed andgasified at high temperatures. Inorganic water glass exceptionally doesnot undergo decomposition. When such thermal decomposition occurs in thecomposite wire during heattreatment, the pressure inside the wirebecomes high owing to the gas generated, and may lead to the rupture ofthe outer tube metal, which in turn results in the failure f thesubsequent processing.

The organic binder used in the present invention also undergoes thisthermal decomposition. Accordingly, if a bundle of material wires coatedwith the abovedescribed kneaded mixture of the separator and the binderis directly inserted in the outer tube metal, it cannot beheat-treatedin the subsequent step. To avoid this, after coating the kneaded mixtureon the material wires, they are heated to a temperature above thethermal decomposition temperature or combustion temperature of theorganic binder to gasify the binder almost completely and release it. Atthis time, liquid such as water or alcohol is also evaporated. Afterthis heattreatment, only the separator remains. For example, a

separator comprising the powders of clay mineral has hydratingproperties, and when it is coated on material wires together with waterand a binder, it is in the state of being lightly sintered even afterthe dissipation of water and the binder by heating. Thus, the separatorremains on the surfaces of the material wires while having somestrength, and the object of coating the material wires with theseparator can be achieved.

Thus, in accordance with this invention, the separator is kneaded withan organic binder and a liquid to render it readily adhesive to thesurfaces of material wires. The kneaded mixture is coated by a suitablemethod, and before insertion of the coated wires'in an outer tube, theliquid and the binder are removed by evaporation, decomposition,gasification or burning, leaving only the separator on the surfaces ofthe material wires.

Table 2 shows typical organic binders identified by chemical formulaeand also the amounts of the binders necessary for incorporation in a ca.3:7 mixture of talc powders as the separator and water as the liquid.

TABLE 2 Chemical fromulae (nNa O'mSiO or nK O'mSiO is also suitable asthe Now, the description will be directed to the case of producing acomposite wire continuously while coating the surfaces of material wireswith a separator using such an organic or inorganic binder. A separatormixture having high viscosity is placed in a coating tank as shown inFIG. 6. Front and back walls 15 and 16 ofthis tank have a plurality ofholes 17 same in number as the material wires to be inserted. Thediameter of each of these holes determines the thickness of theseparator to be coated, and should suitably be about (the diameter 7 ofthe material wire) (the required coat thickness multiplied by 2) 0.05.

Since the thickness tends to become larger with higher viscosity of theseparator mixture, the viscosity, hole diameter, and the coat thicknessshould be determined optionally. The material wires are passed throughthe holes 17 of the walls 15 and 16. During this operation, the materialwires pass through the separator mixture having high viscosity and arethus coated with the separator mixture at their surfaces. By passagethrough the outlet holes, the thickness of the. coat is adjusted to acertain desired value. By inserting in tandem a bundle of the coatedmaterial wires in metal pipe, a composite wire can be obtained. It ishowever necessary to heat and dry them before insertion. The reasonistwofold.

l. The separator mixture solidifies upon heating, and firmly adheres tothe surfaces of the material wires.

2. When heat-treatment is desired after drawing the composite wire,water in water glass, or water incorporated as a solvent for the binder,and adsorbed water of the fine mineral powders are released in advancefrom the surfaces of the material wires and the organic binder is alsoreleased by decomposition. This prevents the evolution of gas inside thecomposite wire during heat-treatment.

This heating and drying can be carried out using a tubular furnaceprovided at the rear of the coating tank shown in FIG. 6, through whichthe composite wire is passed for one minute to 30 seconds at 300 to600C.

The material wires which have been coated with the separator and driedare finished into fine metallic filaments through the steps shown inFIGS. 1 to 3.

As is shown in FIG. 1, an outer tube metal 3 is coated on the outerperipheries of a bundle of a plurality of material wires 1 coated withseparator 2 on the surfaces, to form a composite wire. The compositewire is then, as shown in FIG. 2, subjected to a diameter reductiontreatment by drawing or heat-treatment, etc., until the diameter of eachcore wire reaches a desired value. Then, the outer tube metal 4 of thefinal composite wire shown in FIG. 2 is separated and removed by theabove-mentioned mechanical method or a chemical or electrochemicalmethod. The core filaments l are readily separated from one another bythe separator 2, and fine metallic filaments 1 such as shown i FIG. 3can be obtained.

The production of brass-plated fine steel filaments in accordance withthe above-described method will now be described.

The most important thing in obtaining a bundle of fine filaments byheat-treatment and drawing a composite wire consisting of a bundle ofbrass-plated steel wires inserted in an outer tube is that during theheattreatment, the zinc component in the brass-plated layer isevaporated, and after the heat-treatment, only the copper remains orbrass contains a very small amount of zinc component. This phenomenonoccurs because the vapor pressure of zinc is as high as 0.313 atmosphereat 800C. It has long been thought that the control of atmosphere is noteffective for the heattreatment of a brass article, and there is no waybut to perform the heat-treatment in a slightly oxidizing atmosphere ata temperature not higher than 450C, while forming a thin layer of oxidesof zinc and copper on the surface of the article.

According to the present invention, a mixture of a separator with 1 byweight of'zinc powders is coated on the surfaces of brass-plated steelwires and inserted in an outer tube. After the repetition ofheattreatment and drawing operations, the outer tube is mechanically orchemically removed, to form a bundle of brass-plated fine steelfilaments.

Usually, a separator not containing zinc powders is coated on thesurfaces of brass-plated steel wires, and the coated wires are insertedin an outer tube to form a composite wire. The composite wire is drawn,and when it is subjected to a patenting heat-treatment during thedrawing process, it is performed at 800 to 850C. By this heating, zincpresent in the brass-plated layer is gasified into spaces among theparticles of the separator, and zinc is eliminated from the brass. Inorder to prevent this, a small amount of zinc powders is mixed with theseparator in advance. By this, zinc is gasified at the time ofheat-treatment of the composite wire to increase the partial pressure ofzinc. If the pressure is above the equilibrium vapor pressure of zinc,zinc present in the brass-plated layer is not gasified. This is a theoryby which the climination of zinc from the brass-plated layer isprevented in the present invention. 7

If the amount of zinc powders to be mixed with the separator is below 1%by weight, the above-mentioned elimination of zinc cannot be fullyprevented. If, on the other hand, the amount of zinc powders is above10%, the effect of preventing zinc elimination does not appreciablyincrease, but rather impairs the function of the separator. It issometimes not necessary to use the separator or binder described above.When a very compact layer of an oxide of iron is formed on the surfacesof steel wires, such steel wires, made into a composite wire, can befully drawn, and the bonding of the core filaments to one another in thecomposite wire can be prevented.

In some way or other, this differs somewhat from the conditionsnecessary for the separator as described above. An iron oxide as theseparator is firmly bonded to the surfaces of the material wires.Generally, it is considered that wires not having some oxide on theirsurfaces cannot be produced, but in' the present invention, thisphenomenon is positively utilized. The iron oxide cannot be expected tohave cleavability or plasticity as mentioned in (e) above, but since theoxide is firmly bonded to the surface, the oxide on the surface isbroken as the wire is being drawn. Thus, the oxide is made into fineparticles and present among the individual core wires, thus covering thesurfaces of the wires uniformly. If the iron oxide forms too thick alayer in the form of scales, the frictional force between the wires isreduced, and the force is not transmitted at the time of the drawing ofthe composite wire. However, a compact oxide coating of a thicknessabout 0.0005 to 0.002 mm is effective. In the case of a soft metal suchas copper or aluminum, a coating of its oxide cannot be expected to havethe effect of a separator if the degree of surface reduction of thecomposite wire increases. When material wires obtained by coating thesurfaces of brass-plated steel wires with the oxides of zinc and copperin a thickness of about 0.0005 mm are made into a composite wire and thecomposite wire is subjected to a surface reduction treatment withoutheattreatment, the core filaments are not bonded to one another. This iseffective when the plated layer is very thin, for Example, not more than0.005 mm in a material wire. If this layer becomes thicker, the oxidecoating is broken, and the plated layers are bonded to one another.Furthermore, heat-treatment promotes this bonding further. Thus, onlyunder the specific limited conditions, a compact oxide layer on thesurface of wire acts as a separator.

Now, the invention will be illustrated by the following Examples.

EXAMPLE 1 A well kneaded mixture of fine talc powder, water, andcarboxymethyl cellulose in a ratio of 30:65:5 was placed in a coatingtank 14 having 61 holes 17 with a diamter of 0.7 mm on both walls 15 onthe inlet side and 16 on the outlet side as shown in FIG. 6. Sixty-oneannealed 0.80% carbon steel wires having a diameter of 0.6 mm werepassed through the tank via the holes. The kneaded mixture on thematerial wires were squeezed by the holes 17 on the outlet side of thecoating tank, and coated uniformly on the surfaces of the materialwires. Then, the material wires were passed continuously through aheated furnace kept at 500 to 600C. Water was evaporated there, andcarboxymethyl cellulose was decomposed and gasified. The white dried andsolidified talc was uniformly adhered to the surfaces of the materialwires in a thickness of 0.05 to 0.1 mm. These 61 wires were charged intoa fabricating apparatus for fabricating a mild steel tape into a pipeform and a seam welding apparatus provided in tandem, and a compositewire in which the core wires were enclosed with an outer tube of iron(outer diameter 6.5 mm, pipe thickness 0.6 mm) was continuouslyobtained. The composite wire was cold drawn until the outer diameterreached 4.5 mm, heated at 850C for 5 minutes, cooled for 1 minute inlead at 450C., and air cooled (the so-called continuous patentingtreatment). Further, the drawn composite wire was cold drawn until theouter diameter reached 0.5 mm. The outer tube metal of this thincomposite wire was removed by the mechanical method described above.Each of the core filaments in the tube had an outer diameter of about0.045 mm. Since the core filaments were separated from one another bytalc used as a separator, there could be obtained a yarn of 65 finesteel filaments with an outer diameter of 0.045 mm.

EXAMPLE 2 A kneaded mixture of fine bentonite powders, water andglycerin in a ratio of 50:40:10 was coated on material wires in the sameway as in Example 1. The coated wires were then passed through a heatingfurnace at 400 to 450C. to evaporate water and decompose and burnglycerin. Then the same operation as in Example 3 was performed to givea yarn of 61 fine steel filaments with an outer diameter of 0.045 mm.

EXAMPLE 3 A separator kneaded mixture consisting of fine talc powder andwater glass in a ratio of 2:l was placed in a coating tank of the typeshown in FIG. 6 in which the diameter of each holes on the outlet sidewas adjusted to 0.7 mm. Ninety-one annealed 0.8% carbon steel wires witha diameter of 0.6 mm were passed through the coating tank, and thencontinuously heated in a tubular furnace kept at 500C for a heating timeof 30 seconds. The treated wires were inserted in a mild steel tubehaving an outer diameter of 10.0 mm and a thickness of 0.5 mm in thesame way as in Example 3. At this time, a 0.04 mm thick coating of theseparator was adhered to the surfaces of the material wires.

The composite wire obtained was cold drawn until the outer diameterreached 3.9 mm, and then subjected to a patenting treatment at anaustenitization temperature of 800C and a lead bath temperature of 500C.The treated composite wire was further drawn to an outer diameter of 2.0mm, and subjected again to the patenting treatment under the sameconditions. The composite wire so treated was cold drawn until the outerdiameter reached 0.6 mm. By the same method as in Example l, the outertube metal was removed, and there was obtained a yarn of 91 separatedfine carbon steel filaments with a diameter of about 0.055 mm.

EXAMPLE 4 The procedure of Example 3 was repeated except that bentonitewas used instead of talc. There was obtained a yarn of 91 fine steelfilaments having a diameter of about 0.055 mm.

EXAMPLE 5 A kneaded separator mixture consisting of fine kaolinitepowders, water glass and water in a weight ratio of 3:l:0.5 was placedin a coating tank of the type shown in FIG. 6 in which the diameter ofeach holes on the outlet side was adjusted to 0.60 mm. Ninety ne an:nealed A151 304 Type stainless steel wires with a diameter of 0.5 mmwere passed through the coating tank via the holes, and thencontinuously heated and dried in a tubular furnace held at 300C for aheating time of 30 seconds.- The treated wires were continuouslyinserted in a mild steel pipe having an outer diameter of 9.5 mm and athickness of 0.7 mm to form a composite wire. At this time, a ca. 0.03mm thick coating of the separator was adhered to the surfaces of thematerial wires. Without heat-treatment, this composite wire was colddrawn until the outer diameter of the tube reached 1.55 mm.

The composite wire was then subjected to the same mechanical separationas in Example 1 to form a yarn of fine stainless steel filaments with adiameter of about jected to diameter reduction treatment by a die untilEXAMPLE 6 An adhesive kneaded mixture of fine talc powders, water methylcellulose and zinc powders in a weight ratio of 2025512223 was coated onthe surfaces of heattreated 61 brass-plated (Cu:Zn=7:3; amount of platedbrass 2L0 g/kg) 0.8% carbon steel wires in a thickness of 0.004 to 0.05mm, using the same apparatus as used in Example 1. The coated wires werecontinuously passed through a tubular furnace held at 500 to 600C for aheating time of about 30 seconds, thereby to evaporate water and burnmethyl cellulose. The material wires were continuously inserted in amild steel tube with a diameter of 12 mm and a thickness of 0.6 mm toform a composite wire. The composite wire was subthe diameter reached6.5 mm. All of the abovd steps were performed in tandem. The compositewire was cold drawn until its outer diameter reached 3.0 mm, and washeated at 800C for 4 minutes, and then immersedin lead at 450C for 1minute (patenting treatment). The treated composite wire was cold drawnuntil the outer diameter reached 0.55 mm. By the same method as inExample 1, the outer tube metal was mechanically removed. There wasobtained continuously a yarn of fine brass-plated steel filamentscontaining a uniform and smooth plated layer and having the followingproperties.

61 62.3 microns l.2 microns 282.5 l'Cg/mm Number of core filaments peryarn: Diameter of the core filament: Tensile strength:

Elongation: 1.4% Brass ingredients: Cu 14.7 g/Kg Zn 6.3 g/Kg Total 2l.0g/Kg (Cu:Zn=z30) COMPARATIVE EXAMPLE EXAMPLE 7 As material wires therewere used 0.70% carbon steel wires having a diameter of 0.6 mm which hadbeen austenitized at 850C for one minute in a non-oxidizing atmosphere,and then immediately, immersed in a lead bath at 500C for 30 seconds.Since these material wires were exposed to a slightly oxidizingatmosphere for about 0.5 second between the heating furnace and the leadfurnace, a compact iron oxide layer of a thickness 0.00050.00l mm wasformed on the surface. Sixty-one such steel wires were inserted in amild steel tube having a thicness of 0.6 mm and a diameter of 7.5 mm toform a composite wire. The composite wire was subjected to the samesurface reduction treatment and heat-treatment as in Example 1, and theouter tube metal was removed in the same way as set forth in Example I.There was obtained a yam of 61 fine steel filametns with a diameter of0.045 mm.

EXAMPLE 8 Steel wires which had been subjected to the same patentingtreatment as in Example 7 were pre-treated to remove oxide film,copper-plated and zinc-plated in tandem. The wires were thenelectrically heated at 400 to 450C for l to 2 seconds to diffuse copperand zinc and 7/3 brass-plated steel wires were obtained. Since thisdiffusion treatment was performed in air, very thin layers (less than0.0001 mm) of copper and zinc oxides were formed on the surfaces of thewires.

A composite wire was produced from 61 such steel wires in the same wayas set forth in Example 7, and then drawn by a die withoutheat-treatment until the outer diameter reached 1.3 mm. The outer tubemetal was mechanically removed in the same way as set forth inExample 1. There was obtained a yarn of fine brassplated steel filamentswith a diameter of 0. 127 mm having the same brass-plating components asin the material wires.

What is claimed is:

l. A method of producing fine metallic filaments which comprises coatingthe fine powder of a mineral selected from the group consisting of amineral having a pyrophilite-type crystal structure, a montmorillonitemineral, a kaolinite mineral, and a diatomaceous earth, as a separator,on the surfaces of material wires, covering a bundle of a plurality ofsaid wires with, an outer tube metal, drawing the composite wireobtained and if desired, heat-treating the composite wire, andthereafter, separating the outer tube metal from the core filaments ofthe composite wire, said separator preventing the metallic bonding ofthe core filaments to each other during the drawing or heat treatmentoperation,

wherein the step of coating said separator on the surfaces of themineral wires comprises coating the surfaces of the mineral wires with akneaded mixture having a moderate viscosity consisting of the finepowders of a mineral, an organic binder, and water, and then passing thecoated material wires continuously through a heating furnace, to therebyremove said organic binder in said water by gasification.

2. The method of claim 1, wherein the step of coating the separator onthe surfaces of the material wires comprises coating the surfaces of thematerial wires with a kneaded mixture having moderate viscosityconsisting of the fine powders of a porous mineral, a binder and aliquid or a tacky liquid, and then passing the coated material wirescontinuously through a heating furnace thereby to remove said liquid,tacky liquid, and binder by gasification.

3. The method of claim '1, wherein said organic binder is a memberselected from the group consisting of carboxymethyl cellulose,hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol andglycerine.

4. The method of claim 1 wherein the fine metallic filaments are finebrass-plated steel filaments and the separator contains one to tenpercent by weight of zinc powders, the coating of the separatorpreventing the evaporation of the zinc component of the brass-platedlayer during the heat treatment.

1. A method of producing fine metallic filaments which comprises coatingthe fine powder of a mineral selected from the group consisting of amineral having a pyrophilite-type crystal structure, a montmorillonitemineral, a kaolinite mineral, and a diatomaceous earth, as a separator,on the surfaces of material wires, covering a bundle of a plurality ofsaid wires with, an outer tube metal, drawing the composite wireobtained and if desired, heat-treating the composite wire, andthereafter, separating the outer tube metal from the core filaments ofthe composite wire, said separator preventing the metallic bonding ofthe core filaments to each other during the drawing or heat treatmentoperation, wherein the step of coating said separator on the surfaces ofthe mineral wires comprises coating the surfaces of the mineral wireswith a kneaded mixture having a moderate viscosity consisting of thefine powders of a mineral, an organic binder, and water, and thenpassing the coated material wires continuously through a heatingfurnace, to thereby remove said organic binder in said water bygasification.
 2. The method of claim 1, wherein the step of coating theseparator on the surfaces of the material wires comprises coating thesurfaces of the material wires with a kneaded mixture having moderateviscosity consisting of the fine powders of a porous mineral, a binderand a liquid or a tacky liquid, and then passing the coated materialwires continuously through a heating furnace thereby to remove saidliquid, tacky liquid, and binder by gasification.
 3. The method of claim1, wherein said organic binder is a member selected from the groupconsisting of carboxymethyl cellulose, hydroxyethyl cellulose, methylcellulose, polyvinyl alcohol and glycerine.
 4. The method of claim 1wherein the fine metallic filaments are fine brass-plated steelfilaments and the separator contains one to ten percent by weight ofzinc powders, the coating of the separator preventing the evaporation ofthe zinc component of the brass-plated layer during the heat treatment.